The invention relates to expander rollers (also called rotary stretchers) for webs of paper, textile material, foil or the like.
Expander rollers are used to treat webs of flexible material which are being paid out by supply rolls and/or during winding of webs onto takeup rolls. As a rule, an expander roller has a core of metallic or other suitable material and an outer layer which has an external web-engaging surface designed to stretch the adjacent portion of the running web in response to rotation of the core. The purpose of the expander roller is to preferably stretch the running web in a direction from the center toward both marginal portions in order to eliminate folds, creases and/or other irregularities or to prevent the development of such irregularities. Many types of webs, such as paper webs, webs of textile material webs of metallic or plastic foil, webs of interlaced fibers (e.g., fleece) and the like cannot be processed at all if they develop longitudinally extending and/or otherwise oriented fold lines, creases and/or other unevennesses. An expander roller applies to the adjacent portion of the running web forces acting in the axial direction of the core, or having components extending in such direction, to ensure that the width of the running web increases or tends to increase in order to eliminate creases, fold lines or similar irregularities (hereinafter called creases for short) or to prevent the development of creases while the web is being advanced from a preceding station to the next-following station.
As a rule, the external surface of the outer layer of a conventional expander roller has one or more helical profiles, preferably two profiles which are mirror images of each other with reference to a plane extending between the two profiles at right angles to the axis of the core. Thus, the lead or pitch of one of the profiles is that of a right-hand thread and the lead of the other profile is that of a left-hand thread. Each profile tends to expand the material of a running web from the center toward the respective marginal portion. It is also known to provide the outer layer of a standard expander roller with a single helical profile; such configuration of the external surface of the outer layer also furnishes a desirable stretching or expanding action at right angles to the direction of advancement of the web.
In accordance with a heretofore known proposal, the helical profile or profiles are obtained by grinding or otherwise machining one or more helical grooves into the external surface of a one-piece outer layer which surrounds the core of the expander roller. The outer layer often consists of rubber. Such expander rollers exhibit the advantage that the outer layer produces a highly satisfactory expanding or stretching action and that the core can be driven in a rather simple and inexpensive way in contrast to the cores of certain other conventional expander rollers which employ arcuate cores and arcuate outer layers, i.e., wherein transverse stretching of the running web is achieved as a result of training the web over a roller having a curved axis.
A drawback of conventional straight expander rollers with outer layers of rubber or the like is that the machining of profiles into the external surfaces of the outer layers is a time-consuming and costly procedure. Moreover, the versatility of such rollers is not entirely satisfactory, i.e., a particular roller is capable of stretching only a single web or a series of webs having a certain width, a certain thickness, a certain flexibility or being in contact with a predetermined percentage of the external surface of the outer layer. Therefore, it is necessary to store a substantial supply of discrete expander rollers in order to ensure that a proper roller will be available when the treatment of webs of one type is completed and the machine or apparatus employing one or more expander rollers is to be set up for the processing of different types of webs.
It was further proposed to replace the one-piece outer layer of rubber or the like with an outer layer which consists of or contains a helically convoluted strip or band. The exposed side of the convoluted band has a longitudinally extending protuberance which constitutes a helix and engages the running web of textile or other material in the course of a stretching operation. The protuberance further serves as a reinforcing rib for the major portion of the strip or band which is convoluted onto the core of such expander roller. A drawback of this proposal is that the making of a band or strip with a protuberance involves considerable expenses. Furthermore, the outwardly projecting helical protuberance of the convoluted strip or band is likely to damage or deface a relatively thin and sensitive running web of paper, foil or the like. Therefore, such expander rollers failed to gain widespread acceptance in textile, paper making, paper processing and other industries where webs of paper or other flexible material must be convoluted onto or unwound from rolls or reels without the development of creases or for the express purpose of eliminating existing creases.